It is well known that upon the color development of a silver halide photographic light-sensitive material, after exposure, an oxidized aromatic primary amine developing agent can be reacted with a dye forming coupler to obtain a color image.
It is also known that, for the color development of a silver halide color photographic material, an oxidized aromatic primary amine color developing agent can be reacted with a coupler to form a dye such as an indophenol, an indoaniline, an indamine, an azomethine, a phenoxazine, a phenazine, and the like, thus forming a color image. In this procedure, the subtractive color process is ordinarily used for color reproduction, and silver halide emulsions which are selectively sensitive to blue, green and red light, and yellow, magenta and cyan color image formers, which are respectively the complementary colors of blue, green and red, are employed. For example, a coupler of the acylacetanilide or benzoylmethane type is used for forming a yellow color image; a coupler of the pyrazolone, pyrazolobenzimidazole, cyanoacetophenone or indazolone type is generally used for forming a magenta color image; and a phenolic coupler, such as a phenol and a naphthol, is generally used for forming a cyan color image.
Color couplers must satisfy various requirements. For example, it is necessary that they have a good spectral property and provide a dye image having excellent stability to light, temperature, and humidity for a long period of time upon color development.
It is also required in a multilayer color photographic light-sensitive material that each coupler is fixed in a layer separated from each other in order to reduce color mixing and improve color reproduction. Many methods for rendering a coupler diffusion-resistant are known. One method is to introduce a long chain aliphatic group into a coupler molecule in order to prevent diffusion. Couplers according to such a method require a step of addition to an aqueous gelatin solution by solubilizing in alkali, or a step of dispersing in an aqueous gelatin solution by dissolving in an organic solvent having a high boiling point, since the couplers are immiscible with an aqueous gelatin solution. Such color couplers may cause crystal formation in a photographic emulsion. Furthermore, when using an organic solvent having a high boiling point, a large amount of gelatin must be employed since the organic solvent having a high boiling point softens an emulsion layer. Consequently, this increases the thickness of the material even though it is desirable to reduce the thickness of the emulsion layer.
Another method for rendering a coupler diffusion-resistant is to utilize a polymer coupler obtained by polymerization of a monomeric coupler in the form of a latex. An example of a method of adding a polymer coupler in a latex form to a hydrophilic colloid composition is a method in which a latex prepared by an emulsion polymerization method is directly added to a gelatino silver halide emulsion and a method in which an oleophilic polymer coupler obtained by polvmerization of a monomeric coupler is dispersed in a latex form in an aqueous gelatin solution. Some examples of the former emulsion polymerization methods include an emulsion polymerization method in an aqueous gelatin phase as described in U.S. Pat. No. 3,370,952 and an emulsion polymerization method in water as described in U.S. Pat. No. 4,080,211. An example of the latter method in which an oleophilic polymer coupler is dispersed in a latex form is described in U.S. Pat. No. 3,451,820. The method of adding a polymer coupler in a latex form to a hydrophilic colloid composition has many advantages in comparison with other methods. For example, the deterioration of strength of the film formed is prevented, because the hydrophobic substance is in a latex form. Also, since the latex can contain coupler monomers in a high concentration, it is easy to incorporate couplers in a high concentration into a photographic emulsion, and the thickness of the emulsion layer can be reduced and, thus, the sharpness is improved because the increase of viscosity is small. Furthermore, color mixing is prevented, since a polymer coupler is completely immobilized and the crystallization of couplers in the emulsion layer is small.
With respect to the addition of these polymer couplers in a latex form to a gelatino silver halide emulsion, there are described, for example, 4-equivalent magenta polymer coupler latexes and methods of preparation thereof in U.S. Pat. No. 4,080,211, British Pat. No. 1,247,688, and U.S. Pat. No. 3,451,820, copolymer latexes with a competing coupler in West German Pat. No. 2,725,591 and U.S. Pat. No. 3,926,436 and cyan polymer coupler latexes in U.S. Pat. No. 3,767,412 and Research Disclosure, No. 21728 (1982).
However, these latexes of polymer couplers have problems to be dissolved as well as many excellent features as described above. It should be noted that it has been strongly desired to reduce the formation of fog in unexposed areas and the stability to humidity and heat during storage. The problems include the following:
1. The fog in unexposed areas of color photographs obtained by color development processing is high.
2. The stability tb humidity and heat in the photographic light-sensitive material during storage is poor, and thus sensitivity and gamma of the dye image formed are low.